Sewer pipe and method of fabrication



Oct. 7. 1969 w. c. oLsoN 3,470,918

SEWER PIPE AND METHOD OF FABRICATION Filed Jan. 27, 1966 2 Sheets-Sheet l Oct. 7. 1969 w, cQoLsoN 3,470,918

SEWER PIPE AND METHOD OF FABRICATION Filed Jan. 27, 1966 2 Sheets-Sheet S;

Tre/75A United States Patent M U.S. Cl. 138--165 6 Claims ABSTRACT 0F THE DISCLOSURE A pipe forming apparatus travels in the bottom of a ditch and U-shaped acid resistant plastic sheets are successively issued from the rear end of the apparatus andl connected edge to edge with the two ends of each sheet directed downwardly. Concrete is then poured over the plastic sheets to form a sewer pipe with the opposite lower ends of the sheets embedded in the concrete and the remaining portions of the sheet serving as liners for the concrete pipe.

This invention relates to a sewer pipe and, more particularly, relates to a concrete sewer pipe having an acidresistant plastic liner.

It is well known that concrete deteriorates when subjected to the corrosive fumes of sewage largely because the fumes includes sulfuric acid 'but a concrete sewer pipe is practical if it is lined with a suitable impermeable inert material such as a suitable acid-resistant plastic. It is also known, as set forth in the Edward Patent 2,243,273, that since it is primarily the fumes and not the liquid sewage that attacks the concrete, the inert liner need extend no lower than the minimum liquid level in the sewer line.

All of the prior art procedures within my knowledge for fabricating such a composite sewer ppie, however, are not continuous fabrication procedures and therefore are not economical in comparison to well known methods of continuously forming a concrete water pipe in a single operation. A continuous method of fabricating an unlined concrete pipe is set forth, for example, in the two Tunsen Patents 2,731,698 and 3,106,760, which prior art disclosures are hereby incorporated into the present disclosure by reference.

In the Tunsen fabrication procedure, a ditch is dug and an apparatus is placed in the ditch for progressive movement along the ditch by means of a cable and winch mechanism. The apparatus has a hollow arcuate mandrel shaped in accord with the desired inner circumference of the concrete pipe and has an upper wall spaced above the mandrel to shape the outer top surface of the concrete pipe. In addition, the moving apparatus has a hopper to receive concrete for' forming the concrete pipe and has suitable means to vibrate the apparatus to cause the concrete to settle and become compact. As the apparatus moves along the ditch, successive metal form sheets are added by introduction over the hollow mandrel and concrete from the hopper flows over and around the successively added form sheets. A single vibrator may be located on the above mentioned upper wall of the apparatus or on the hopper or a plurality of Vibrators may be provided at spaced points on the apparatus.

The metal form sheets are interconnected end to end to form a continuous series with the initial end of the series anchored to keep the series stationary as the apparatus moves along the ditch. As the successive arcuate metal form sheets emerge from the apparatus, suitable transverse struts are placed inside the sheets to reinforce the sheets against the weight of the newly poured concrete and after the concrete sets both the struts and the metal form sheets are withdrawn from the interior of the concrete pipe.

3,470,918 Patented Oct. 7, 1969 To make it possible to remove the metal form sheets readily from the cured concrete each sheet is of less circumferential extent than the inner circumference of the concrete pipe so that the sheet may be readily contracted by exure to a diameter less than the inside diameter of the finished concrete pipe. Since the concrete tends to adhere tenaciously to the metal form sheets and the adherence is increased by the vibration that compacts the concrete, the vibration must be kept moderate to avoid makingit too difficult to dislodge the metal form sheets.

With reference to the present invention, wherein a suitable acid-resistant plastic sheet material permanently lines a concrete sewer pipe is would be a-dvantageous to have the concrete adhere tenaciously to the liner, but unfortunately concrete does not tend to adhere to the plastic sheet and therefore the liner cannot be held in place by adhesion of the concrete. This problem of keeping the liner snugly in place has been solved by using curved plastic sheets of less circumferential extent than the inner circumference of the concrete pipe, with two lower longitudinal edge portions of the sheets spaced apart to expose the concrete below the anticipated minimum level of the liquid sewage. Adequate anchorage of the liner sheet is accomplished simply by bending the lower longitudinal edge portions of the sheets spaced apart to expose the concrete below the anticipated minimum level of the liquid sewage. Adequate anchorage of the liner sheet is accomplished simply by Abending the lower longitudinal edge portions of the sheet to diverge outwardly from the inner circumference of the concrete pipe so that the longitudinal edge portions of the sheet become embedded in the concrete for permanent anchorage of the liner sheet. The invention takes advantage of the well known fact that concrete contracts as it cures, the shrinking of the concrete resulting in snug contact between the concrete and the liner sheet.

To carry out the new procedure for continuous fabrication of a concrete sewer pipe, an apparatus is used that is constructed in the gneral manner disclosed in the two Tunsen patents and the liner sheets are successively introduced and interconnected in the same general manner as the temporary metal form sheets in the prior art procedure. The Vibratory means of the apparatus may be operated at as high an energy level as may be desirable for thoroughly compacting the cement.

An important feature of the invention is that the vibration of the apparatus is transmitted to the plastic liner sheets and thereby serves two new purposes. One of the new purposes is to drive the divergent lower longitudinal edge portions of the plastic sheets into the newly poured concrete that forms the pipe. The other of the new purposes of the vibratory means is to cause the local formation of slurry in the concrete to envelope and seal the lower divergent longitudinal edge portions of the plastic sheets.

v Arcuate struts are employed temporarily inside the newly formed sewer pipe to reinforce the liner sheets against the weight of the concrete until the concrete cures. One feature of the invention is the use of reinforcing struts of such shape as to tend to spread the liner sheets and thus tend to drive the divergent lower edges of the sheets into the concrete. An important unexpected advantage of the use of the temporary reinforcement struts is that the struts provide downward diagonal paths along which the vibratory forces are transmitted and directed against the inner surfaces of the liner sheets to result in the .application of a desirably high level of vibratory energy at the lower longitudinal edges of the sheets.

A further feature of the invention is the concept of encouraging penetration of the divergent lower edge portions of the liner sheets into the concrete by employing sheet material that has plastic memory and by initially forming the liner sheets to a somewhat larger radius of curvature than the planned inside radius of the concrete pipe. The tendency of the plastic liner sheet to expand in diameter is concentrated at the lower free divergent edges of the sheets.

The various features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

In the drawings, which .are to be regarded as merely illustrative:

FIG. 1 is a diagrammatic longitudinal sectional view of an apparatus of the character described moving along the bottom of a ditch in the process of continuously forming a lined sewer pipe;

FIG. 2 is a fragmentary perspective view showing how the liner sheets are interconnected end for end in a linear series;

FIG. 3 is a fragmentary sectional view taken along the line 3 3 of FIG. 2 showing how two successive plastic sheets in the series interlock with each other;

FIG. 4 is an enlarged sectional view showing how acidresistant adhesive material is placed in a groove in one sheet prior to the mechanical interlocking of the two sheets;

FIG. 5 is a side elevation of a temporary reinforcement strut that may be used in the practice of the invention;

FIG. 6 is a sectional view showing the cross-sectional configuration of a trench in which the lined concrete sewer pipe is to be formed;

FIG. 7 is a sectional view taken along the line 7 7 of FIG. 1 showing the initial flow of concrete from the hopper over an arcuate plastic liner sheet;

FIG. 8 is a similar view at a more advanced stage of the ow of the concrete;

FIG. 9 is a similar view showing the finished pipe in cross section and showing a reinforcement strut being dislodged for removal; and

FIG. 10 is a cross-sectional view of a finished sewer pipe in actual service.

The invention employs a plurality of arcuate plastic liner sheets 10 of the character shown in FIGS. 2 and 3. Each liner sheet 10 is made of a suitable acid-resistant plastic and for this purpose may be made of an iso phthalic base polyester resin, for example a Chevron Type 5893 polyester resin manufactured by the California Chemical Co. Each of the liner sheets is preferably reinforced by embedded glass bers and is formed to a radius of curvature that is slightly larger than the desired radius of curvature of the inside of the sewer pipe.

The circumferential extent of each of the liner sheets 10 is substantially less than the inner circumference of the sewer pipe because the liner is not intended to cover the bottom inner surface of the concrete pipe below the minimum level of the liquid sewage. Since it is intended that the two spaced lower longitudinal edge portions 12 of the liner sheet will be embedded in the concrete wall of the pipe, these longitudinal edge portions are bent outward to diverge from the curvature to which the sheet is formed.

It is essential that the arcuate liner sheets 10 be adapted for interconnection in an end to end relationship to form a continuous series that is capable of withstanding a moderate amount of stress in tension. For this purpose it is contemplated that the sheets will be formed with shoulders, preferably hook-shaped shoulders, to interlock in a positive manner.

In the present embodiment of the invention, one end of each sheet is formed with a radially inwardly offset portion 14 as shown in FIG. 4 and this offset portion is formed with a circumferentially extending groove 15 that is undercut to form a hook-shaped shoulder 16. The other end of the arcuate liner sheet is formed with a radially outwardly protruding rib 1S that is undercut to form a hook-shaped shoulder shaped and dimensioned 4 to make positive engagement with the hook-shaped shoulder 16`of an adjacent arcuate liner sheet.

Since the juncture between two of the acid-resistant liner sheets 10 must be fluid tight and acid resistant, a suitable acid-resistant adhesive 22 is deposited in the groove 15 as shown in FIG. 4 prior to the insertion of the rib 18 of an adjacent sheet into the groove. The adhesive may be, for example, a polyurethane adhesive, or other acid resistant adhesive. It is to be ntoed that the groove 15 is substantially wider than the rib of the complementary rib 18 to provide a desirable degree of freedom for relative movement of the rib in the groove so that two consecutive interlocked liner sheets may be at an angle relative to each other to make it possible for the concrete pipe to curve to gradually change direction wherever such a change in direction is desired.

The apparatus for continuously forming the pipe iS of the character disclosed in the previously mentioned Tunsen patents and is shown diagrammatically in FIG. 1. The apparatus is dimensioned to fit into a ditch of the cross-sectional configuration shown in FIG. 6, the apparatus having a rounded bottom wall 24, two opposite side walls 26 for sliding contact with the side walls of the ditch and a roof 26 interconnecting the two side walls. The roof and side walls forma work space 28 forward of a rigid arcuate hollow mandrel 30 having an outside diameter equal to the desired inside diameter of the finished sewer. A lower portion 32 of the mandrel projects rearward to function as a trowel for shaping the oor of the sewer and an upper arcuate wall 34 above the mandrel serves as a trowel to shape the upper outer surface of the concrete pipe. A suitable upright hopper 35 feeds concrete to the successive plastic liner sheets on the mandrel as the apparatus moves forward or to the right as viewed in FIG. 1. The apparatus is moved slowly forward by means of a cable 36, one end of which is anchored in the ditch and the other end of which is wound onto a power actuated winch (not shown) inside the apparatus.

To start the continuous fabrication of a length of the sewer pipe, an arcuate liner sheet 10 that is to start the series of interconnected liner sheets is suitably anchored in the ditch so that the chain of liner sheets will remain stationary and not be dragged forward by frictional contact with the moving apparatus. FIG. 1 show an interconnected series of liner sheets 10a-10f extending from a remote point of anchorage to and over the mandrel 30. A workman in the work space 28 has just attached a new arcuate liner sheet 10gI to the end of the series. In making this connection the workman applies adhesive 22 to a groove 15 on the rear end of the sheet 10f in the manner shown in FIG. 4 and then `adds the liner sheet 10g to the series by pressing the rib 18 of the new liner sheet into the groove for hook engagement with the hook-shaped shoulder 16 of the liner sheet 101.

With the apparatus moving slowly to the right in FIG. 1, successive arcuate liner sheets 10 are added in the manner described with the hopper 35 depositing concrete on the newly added liner sheets as the liner sheets slide on the surface of the mandrel 30. The newly added concrete ows downward on the opposite sides of the arcuate liner sheets as shown in FIGS. 7 and 8 with the two streams of concrete meeting to complete the configuration of the pipe as shown in FIG. 9. As the arcuate upper wall 34 shapes the top surface of the continuously formed concrete pipe, the apparatus is vibrated in a manner to facilitate ow of the concrete and to cause the concrete to take a compact form without any voids. Any number of vibrators may be mounted on the apparatus for this purpose. FIG. 1 shows a vibrator 38 actuated by a motor 40, the vibrator being mounted on the upper wall 34 to direct pulsating force downward through the newly poured concrete.

As the hollow mandrel 30 of the rightwardly moving apparatus clears the successive liner sheets 10 to expose the inner surfaces of the liner sheets, a workman inside the mandrel at its trailing end mounts temporary reinforcement struts 42 inside the liner sheets to brace the liner sheets against the weight of the concrete. The struts 42 may be positioned at any points along the liner sheets. As shown in FIG. 1 the struts 42 may be positioned advantageously at the junctures of the successive liner sheets.

After the concrete sets, a workman enters the finished sewer pipe to remove the struts 42. FIG. 9 shows how a strut 42 may be dislodged and turned for removal from the sewer pipe.

In the preferred practice of the invention each of the struts 42 is of the configuration shown in FIG. 5. The strut may be made of various materials including metal, plywood and plastics. As shown in FIG. 5, the strut is of open construction for lightness and ease of handling. The strut 42 has an upper arcuate edge 44 of the configuration of a half circle of the same radius as the inner circumference of the sewer pipe and the strut further has two opposite downwardly extending side edges which diverge outwardly from the curvature of the arcuate edge 44. In this instance the two side edges 45 are tangential to the arcuate edge 44 and are substantially vertical when the strut is positioned inside a liner sheet. It is apparent that since the side edges 45 diverge outwardly from the curvature of the upper arcuate edge 44, the two side edges have a spreading effect on the two legs of the liner sheet and thus tend to drive the outwardly bent lower edge portions 12 of the liner sheet into the concrete as may be seen in FIG. 8.

The vibration of the apparatus is transmitted to the regions of the two lower edge portions 12 of the liner sheet along various paths. Thus with the vibrator 38 mounted on the upper wall 34, pulsations or waves of energy are directed downward along the paths of ow of the concrete as indicated by the Outer arrows in FIGS. 7 and 8. The pulsating energy is also directed against each of the newly installed struts 42 to follow diagonal paths through the struts as indicated by the wavey arrows in FIGS. 7 and 8.

It is important to note that since the maximum pressure of a newly installed strut 42 against the surrounding liner sheet 10 is in the region of the two opposite lower corners of the strut where the strut spreads the liner, the vibratory forces are transmitted effectively to the lower corners to promote pulsation of the two opposite legs of a liner sheet. In addition, it is to be noted that the rearwardly extending lower portion 32 of the mandrel is a rigid part of the apparatus and therefore is vibrated along with the upper wall 34. The vibrations of the extension 32 are directed towards the two lower edge portions 12 of a liner sheet and has substantial eiect because the lower portion of the mandrel is quite close to the lower edge portions 12 of the sheet as may be seen in FIG. 8.

It has been found that the vibration of the liner sheets drives their outwardly bent lower portions 12 into the concrete and it has been further found that the vibrating edge portions cause pools of slurry to develop. The pools of slurry are exceptionally rich in cement and result in the edge portions 12 of the sheet-s being effectively sealed in the concrete.

As heretofore stated the concrete shrinks slightly when it cures with the result that the concrete of the finished pipe fits snugly over the plastic liner and desirably places the plastic liner under a certain degree of circumferential compression. As heretofore stated it is contemplated that the two lower edges of the plastic liner will be below the liquid level when the sewer is placed in service. It

has been found, however, that if the liquid level does fall somewhat below the liner to expose some of the concrete to the fu-mes ofthe sewage, no significant deterioration of the c-oncrete occurs because the fumes tend to accumulate in the upper portion of the sewer pipe;

My description herein of the selected practice of the invention in specific detail will suggest various changes, modifications and other departures from my disclosure within the spirit and scope of the appended claims.

I claim: ,1. A liner sheet for lining a concrete sewer pipe wherein the sewer pipe is formed continuously by an apparatus that moves progressively in a ditch longitudinally of the ditch, the apparatus having means to receive concrete for the sewer pipe and having a mandrel to shape the interior ofthe sewer pipe and having an upper wall spaced above the mandrel to shape the upper outer surface of the sewer pipe, whereby successive curved liner sheets may be connected end for end and fed over the mandrel to form a permanent liner in the sewer pipe,

said sheet being a sheet of acid resistant plastic shaped to a given curvature in accord with the inner curvature of the sewer pipe, said sheet being of -a circumferential extent of les-s than the inner circumference of the sewer pipe to line the interior of the sewer pipe, with lower longitudinal edge portions of the sheet spaced apart to leave a bottom portion of the concrete sewer pipe exposed tothe interior of the sewer Plpe,

each of said lower longitudinal edge portions diverging outward from said given curvature for embedment in the concrete of the sewer pipe,

said sheet being adapted at each of its ends for engagement with similar sheets in end to end relation.

2. A liner sheet as set forth in claim 1 made of a polyester resin.

3, A liner sheet as set forth in claim 1 in which the sheet is formed with shoulders at its forward and rearward ends for engagement with shoulders of adjacent sheets to interconnect the sheets.

4. A liner sheet as set forth in claim 3 in which said yshoulders are hook-shaped in cross section to permit successive sheets to hook together.

5. A liner sheet as set forth in claim 1 in which one of the forward and rearward ends of the sheet i-s formed with a transverse groove and the other of the forward and rearward ends of the sheet is formed with a complementary rib to seat in such a groove of another sheet.

6. A liner sheet as set forth in claim 5 in which said groove and rib are shaped to hook together.

References Cited UNITED STATES PATENTS 1,544,592 7/1925 Murray 138-175 1,636,367 7/1927 Illemann 13S-175 XR 2,798,509 7/ 1957 Bergquist 138l45 2,816,323 12/1957 Munger.

3,125,124 3/1964 Daniels et al. 138-141 3,177,902 4/1965 Rubenstein 138-176 3,276,092 10/1966 Pankow 13S-176 XR 3,297,056 1/1967 McLaughlin et al. 13S-145 3,301,278 1/1967 Lander et al 138-145 3,381,718 5/1968 Darrow 138-141 LAVERNE D. GEIGER, Primary Examiner HENRY K. ARTIS, Assistant Examiner U.S. Cl. X.R. 

